[Dave at Pelican Parts]

210F is absolutely in the middle of the normal oil temperature range. Anything lower than 180F is not warm enough, in fact. Your temps should not have caused any problems at all.

Your description makes it sound like the cylinders were seizing in the bores. They shouldn't be, obviously. I wonder if you are running 105mm cast-iron cylinders? I have heard stories of the large cast-iron cylinders distorting given time and heat cycles, and that could possibly cause symptoms like this.

Any way you can talk to the builder of the engine?

--DD